I can’t remember now, and you can save me a trip to the office if you do, but wasn’t Dirac’s conjecture an exercise in Jackson’s book? [We certainly did it as an assignment in first year Classical Electrodynamics, either way.]
Self taught here, specifying sources is pretty much a no go with me. I try to read multiple angles, the stranger ones make great late night reading, and focus on what works. I haven’t published anything...yet.